The present invention generally relates to devices and methods for assisting heart function and, more particularly, devices and methods intended to supplement the natural blood pumping ability of a patient""s native heart.
Two major options exist for treating a weakened or diseased heart. A totally artificial heart may be implanted or a heart transplant may be performed, or a heart assist device may be used to supplement the function of the patient""s natural heart to achieve a total blood flow through the heart which is acceptable. Most of the development in this area has been directed toward completely implantable heart replacements and significantly invasive heart assist devices which are bulky and complicated. There will always be some need for such devices, however, for every patient on the transplant list who may need a totally artificial heart there are fifty less serious cases of congestive heart failure in which the patient survives on other medical therapy. Unfortunately, the conventional medical therapies may not be sufficient to provide a high quality of life for the patient. Completely artificial hearts are also risky due to biological compatibility problems, blood clotting, manufacturing problems and regulatory issues. The surgical operation to install artificial hearts is very complex and, after installation, significant maintenance and follow-up is necessary.
Many patients will succeed with a partial heart assist which increases cardiac output by 20% to 50%. Such a device would well serve patients with idiopathic cardiomyopathy, ischemic cardiomyopathy, ischemic mitral regurgitation and progressive mitral regurgitation. In fact, a partial heart assist device may be completely sufficient for many potential transplant patients. Early installation of a partial heart assist device could unload the heart and prevent the development of congestive heart failure in patients with declining left ventricular function. If the hearts of these patients are partially unloaded with a suitable device, this could entirely avoid the need for surgery. Other patients may be too old for invasive surgery, but could lead higher quality lives with a suitable partial heart assist device. In all patients, aortic and mitral insufficiency (that is, volume overload conditions) are well-tolerated for many years until the heart begins to dilate. It may be desirable to allow these valves to leak to some extent, while unloading the heart and preventing dilation and the need for future surgery.
A large number of patients with ischemic coronary artery disease continue to have pain when they are undergoing maximal drug therapy. This maximal therapy is defined as the point when heart failure symptoms occur. With a suitable heart assist device, drug doses may be increased further while supporting the patient""s heart with a partial heart assist device. Unloading dilated hearts with a partial or supplemental heart assist device may also reduce the risk of fatal arrhythmia and may be an effective adjunct for patients with defibrillators. It may also increase the amount of drug that can be effectively administered for arrhythmia as many of these agents depress contractility. Partial heart assist devices may also be useful after massive infarction to unload the heart and prevent unfavorable remodeling.
Ever since its introduction, the pacemaker has been widely accepted and very successful. The pacemaker is relatively simple to insert and does not require a major surgical operation. It is located superficially in a subcutaneous area of the patient""s chest and is not regarded as highly invasive. As the market for pacemakers has grown, additional features have been added, such as defibrillators and cardioverters. Due to their simplicity and reliability, pacemakers are now inserted for even a suspicion of a potentially dangerous arrhythmia.
It would be desirable to provide a partial assist device or system along with associated methods which provide effective assistance with cardiac output as well as simplicity of design, ease of implantation, low cost and reliability. In essence, it would be desirable to provide a system and methods which combine the intentions of past heart assist devices with the simplicity, reliability, minimal invasiveness and other desirable attributes of a pacemaker-type device. A partial assist device which is only slightly more complex to insert than a pacemaker and that is as reliable, cost effective and as versatile as a pacemaker would increase the quality of life for many additional patients.
In one aspect, therefore, the present invention contemplates a device requiring only a small pocket made subcutaneously over the patient""s chest, such as in the subclavicular region, as in a pacemaker, for housing a blood pump. Preferably, the size, shape and implant location would be similar to a pacemaker. The inflow for the pump is provided by a catheter or other conduit which is inserted into the left side of the heart, such as the left atrium, either by a small thoracotomy, sternotomy or by an endoscopic approach using ports placed in the chest. The cannula will then be passed out of the chest between the ribs and attached to the pump. The outflow from the pump may be completed by sewing a graft from the pump outlet to an artery in the shoulder area, such as an axillary artery, or by connecting a cannula between the pump and the shoulder artery. In short, oxygenated blood will be pumped from the left atrium of the heart to the shoulder artery and into the aorta. Various manners of powering the pump may be provided, such as by using a transcutaneous power supply with internal and external power coils, as known in the medical art, or other power supply either within the patient""s body or outside the patient""s body. An external energy source may be connected to the patient by a harness or belt. As another aspect of the invention, a reliable connection and alignment system is provided for the external portion of the power supply.
In a second aspect of the invention, the goal is to eliminate the intrathoracic part of the procedure. In this operation, the inflow cannula will pass from the axillary vein down the subclavian vein into the right atrium of the heart and across the septum in the left atrium. Blood will be withdrawn from the left atrium retrograde, up the subclavian vein inside the cannula and pumped into the axillary artery or another shoulder artery. The entire procedure may be accomplished from the same subclavicular incision. To augment blood flow, additional drainage catheters may be added from the opposite side of the chest or from the ipsilateral or contralateral neck veins. To simplify this procedure so that maximal blood flow is achieved, it may be easier to provide a large left atrial drainage cannula that occludes the right or left subclavian vein. In this case, however, the patient""s arm may swell if the patient is not provided with a manner of returning blood from the arm. For this purpose, a second cannula, or a separate portion or orifice of the inflow cannula, may be used to pump the venous return from the arm around the obstruction and into the right side of the heart. As another alternative, the blue blood, or venous return from the arm may be mixed with the red blood or oxygenated blood from the left side of the heart and this mixture may be pumped back into the axillary artery. Provided that the left atrial blood is fully saturated, up to 25% venous blood could be mixed with the oxygenated blood or red blood from the left atrium before desaturation occurs.
Each of the procedures performed with products of the invention would require only a small incision in the shoulder area comparable to the size of a pacemaker or defibrillator. A pocket would be made for the pump and, for example, another pocket for a power coil or internal portion of a transcutaneous power supply. The subclavian vein would be cannulated for access to the left atrium of the heart and the outflow of the pump would be connected for fluid communication with the axillary artery or another shoulder artery. All of these portions of the procedure may be accessed through the same incision.
Various additional possibilities for the system and methods of this invention exist, including: 1) the cannulation points may vary, such as by making the artery or vein cannulation points anywhere in the shoulder or neck area, and not specifically in the subclavian vein and axillary artery; 2) when the left atrium is cannulated, the cannula will likely pass between the ribs, however, the cannula could also pass below the ribs, such as through the diaphragm, or above the ribs, such as out the thoracic inlet; 3) the left ventricle may be cannulated instead of the left atrium as a source of oxygenated blood; 4) the pump may be located inside or outside the chest or abdomen and not necessarily in a subcutaneous pocket on the outside of the chest or abdomen; 5) the pump may be implanted in the groin area of the patient and may draw blood from the left atrium or ventricle and return it to the groin area arteries either to the femoral arteries or via a retroperitoneal incision to the illiac arteries; 6) the pump may be located in a tube or in a separate unit and may be of any type and shape; 7) preferably run continuously and in a highly energy efficient manner; and 8) to shut down the system, a cannula associated with the device may be clamped or partly or entirely removed from the patient.
Additional modifications, substitutions, features and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the presently preferred embodiments in conjunction with the the accompanying drawings.